Diarrhoea develops in association with antibiotic treatment in 1% to 44%12 of cases, and ranges from mild episodes that resolve when antibiotics are stopped to serious complications such as toxic megacolon, bowel perforation, and death. Risk is increased with extremes of age, co-morbidity, oral broad spectrum antibiotics (particularly clindamycin, β-lactams, and third generation cephalosporins), prolonged antibiotic duration, previous antibiotic associated diarrhoea, and hospitalisation. Probiotics—live microorganisms that, when administered in adequate amounts, confer a health benefit on the host—are present in products available in shops as foodstuffs, and in formulations used for specific therapeutic purposes. Probiotics are thought to combat antibiotic associated diarrhoea through restoring resistance to colonisation by pathogenic bacteria after the normal colonic microflora have been damaged by antibiotics, by breaking down non-absorbable compounds into absorbable products, by interfering with pathogenic toxins, and by enhancing immunity. Effects of probiotics vary by strain owing to differing resistance to gastric acid and bile, ability to colonise mucosa, and susceptibility to antibiotics.3

Probiotics carry theoretical risks, including infection beyond the gut and transfer of antibiotic resistant genes. However, so far, there have been no reports of bacteraemia or fungaemia attributable to the probiotics in trials included in published systematic reviews.45678910

Lactobacillus bacteraemia is rare and has a low mortality rate.11 Cancer, diabetes, broad spectrum antibiotic therapy, organ transplantation, and abscess may be risk factors for lactobacillus bacteraemia. Twelve cases of lactobacillus bacteraemia have been reported in patients taking a probiotic and 24 cases of fungaemia associated with the probiotic Saccharomyces boulardii. However, many lactobacillus strains are human …

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